fix: align sharing button height with like button

Remove size="sm" from SharingPopupButton to use default button height (h-9)
instead of small size (h-8), ensuring consistent button heights across all
action buttons on video, model, and article pages.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

packages/frontend/src/lib/components/sharing-popup/sharing-popup-button.svelte

@@ -10,7 +10,6 @@ let isPopupOpen = $state(false);
 <Button
   onclick={() => (isPopupOpen = true)}
   variant="outline"
-  size="sm"
   class="flex items-center gap-2 border-primary/20 hover:bg-primary/10 cursor-pointer"
 >
   <span class="icon-[ri--share-2-line] w-4 h-4"></span>